Here are the major advantages of using ColorWasher compared to Levels:

1. ColorWasher offers Auto buttons.
2. ColorWasher offers six color correction algorithms while Levels only uses one which doesn't always produce the best results.
3. ColorWasher lets you sample colors more precisely with the sample area.
4. You only need to sample one area and it doesn't matter if it is located in the midtone, shadows or highlight area.
5. The brightness is automatically kept constant.
6. You can also use various color models to adjust the color manually, e.g. HSL or Color Temperature.